Cartridge with fin deployment mechanism

ABSTRACT

A projectile for a weapon comprises an axially movable firing pin, an initiator actuable when impinged by the firing pin, a plurality of external peripheral fins movable from a radially inward position to a radially outward position when the projectile leaves the weapon, fin engaging means for moving each fin from the radially inward position to the radially outward position and for maintaining each fin in the radially outward position, and internal actuating means for actuating the fin engaging means to engage and thereby move the fins to deploy from the radially inward to the radially outward position as the projectile leaves the weapon.

[0001] The present invention relates to a projectile for a weapon, inparticular a projectile having an improved fin deployment mechanism.

[0002] Projectiles having stabilising fins are well known in the art.When the projectile leaves the barrel of the weapon the fins deploy froma radially inward position to a radially outward position, to providestability of the projectile during flight.

[0003] Various mechanisms by which projectile fins are deployed areknown. For example, fins may be deployed and maintained in a radiallyoutward position by being biassed by springs. When the projectile iswithin the barrel of a weapon the fins are restrained by the internalbarrel wall or a cartridge sleeve in a radially inward position, andwhen the projectile leaves the barrel the fins are no longer restrainedand the springs urge the fins into the radially outward position.However, spring biassed mechanisms have a number of drawbacks. Firstly,they can create manufacturing difficulties, in particular for small armsprojectiles where fitting the springs may involve prohibitively slow orcostly manufacturing equipment and processes, or may even necessitatemanual fitting, particularly for small arms projectiles. In addition,springs can also lose their initial resilience if constrained in acompressed state over a significant period of time, for example duringstorage of a projectile having spring biassed fins after manufacture.This can result in a relatively short shelf-life for the projectile ifthe risk of fin deployment difficulties due to spring failure is to beminimised. Furthermore, springs are conventionally made of thin metalwire, which can corrode over time, resulting in an increased risk ofspring failure.

[0004] The present invention can provide a projectile for a weapon inwhich the fins are deployed and maintained in a radially outwardposition without using springs, and hence can overcome theaforementioned disadvantages of spring biassed fin deploymentmechanisms, for example through improved manufacturing efficiency, andreduced risk of fin deployment failure after storage.

[0005] According to the present invention there is provided a projectilefor a weapon, which projectile comprises:—

[0006] an axially movable firing pin;

[0007] an initiator actuable when impinged by the firing pin;

[0008] a plurality of external peripheral fins movable from a radiallyinward position to a radially outward position when the projectileleaves the weapon;

[0009] fin engaging means for moving each fin from the radially inwardposition to the radially outward position and for maintaining each finin the radially outward position; and

[0010] internal actuating means for actuating the fin engaging means toengage and thereby move the fins to deploy from the radially inward tothe radially outward position as the projectile leaves the weapon.

[0011] The actuating means is positioned internal to the casing, andactuates the fin engaging means following firing of the projectile fromthe weapon. This is conveniently achieved by axial movement of theactuating means towards the fin engaging means in response to theprojectile leaving the barrel of a weapon. When the projectile is firedfrom the barrel of a weapon, the actuating means moves axially away fromthe initiator, and into engagement with the fin engaging means tothereby actuate the latter. The actuating means is preferably biassedtowards the fin engaging means. More preferably, the actuating means isurged by a spring, even more preferably a single central compressionspring, towards the fin engaging means.

[0012] A convenient means by which the actuating means can engage thefin engaging means is via a cam surface, for example a cam surface inthe form of a frusto-conical portion of the actuating means whichnarrows towards the fin engaging means. Thus, as the frusto-conical camsurface moves axially towards and engages the fin engaging means, itexerts radially outward pressure thereon, which radially outwardpressure is transmitted via the fin engaging means to the fins.

[0013] The actuating means may, for example, be in the form of a biassedor unbiassed axially moveable sheath or tube internal to the casing, butpreferably comprises the firing pin, and more preferably comprises thefiring pin biassed towards the fin engaging means. Such an arrangementsimplifies the design and manufacture of the projectile by helping tominimise the number of component parts. Thus, the firing pin can servethe dual purpose of impinging on the initiator to initiate an explosivecharge and thereby detonate the warhead, and of actuating the finengaging means so as to deploy the fins in the radially outwardposition.

[0014] The fin engaging means may take any form which can apply radiallyoutward pressure to the fins. The fin engaging means preferablycomprises a fin engaging pin per fin, each pin being radially moveablerelative to the actuating means, and being disposed between the fin andthe actuating means. Each pin is preferably fashioned to have ahemispherical inner end for engagement with the actuating means, and aconical outer end for engagement with a fin. Thus, in use the inner endof each pin engages the actuating means, and the outer end of each pinengages a fin. Axial movement of the actuating means causes radiallyoutward movement of each pin, which in turn causes each fin engagedthereby to move radially outward. The precise angle of disposal of thepins relative to the longitudinal/rotational axis of the projectile willof course depend upon the precise mechanism of the engagement betweenthe actuating means and the fin engaging means, to maximise mechanicaladvantage of the mechanism, as will be apparent to those skilled in theart.

[0015] The fin engaging means preferably also releasably restrains thefiring pin in a safety position until actuation, and when actuatedallows the firing pin to move into an armed position. The fin engagingmeans can thus provide a safety system for the projectile, whereby thefiring pin is restrained in a safety position in which it cannot impingethe initiator until the fin engaging means is actuated by the actuatingmeans, achieved on firing when the projectile leaves the barrel of aweapon.

[0016] In a preferred embodiment, as described above, the fin engagingmeans comprises pins disposed between the actuating means and the fins.For ease of assembly, the projectile preferably further comprises meansfor moving the fins from the radially outward position to a positionwhich provides improved access to the fin engaging means over the accessprovided to the fin engaging means when the fins are in the radiallyoutward position. The means for moving the fins conveniently comprises ahinge along which the fins are axially movable from a first position toa second position, whereby radial movement of the fins in the secondposition is less restricted than radial movement of the fins in thefirst position.

[0017] The projectile of the present invention preferably also comprisesa casing, which casing has an inner sleeve therewithin adjacent theinner wall thereof for guiding movement of the actuating means and finengaging means. In a preferred embodiment, the inner sleeve compriseslongitudinal slots within which said fin engaging pins are disposed. Theinner sleeve may further provide means for fixing the spring whichbiasses the firing pin to the casing, as described hereinabove.

[0018] The projectile of the present invention preferably also comprisesa firing pin release means within the casing, which release means isaxially moveable relative to the casing away from the initiator, andhelps retain the firing pin in the safety position, i.e. prevents axialmovement of the firing pin towards the fin engaging means prior tofiring of the projectile from a weapon. On firing the projectile in thebarrel of a weapon, the initial acceleration of the projectile causesthe release means to move axially within the casing away from theinitiator, thereby disengaging from the firing pin so it no longerprevents axial movement of the firing pin, and thereby does not preventthe firing pin from moving from the safety position to the armedposition.

[0019] The projectile of the present invention preferable also comprisesfurther safety means for helping to retain the firing pin in the safetyposition prior to firing the projectile from a weapon, by preventingaxial movement of the firing pin away from the initiator. In preferredembodiments of the present invention, the safety means comprises acrushable support element and/or a frangible safety pin.

[0020] The crushable support element is disposed towards the rear of thecasing, i.e. axially opposite the warhead, and supports the firing pinand release means (when present) prior to firing the projectile from aweapon, thereby preventing axial movement of the firing pin and releasemeans (when present). However, on firing the projectile from a weapon,the forces of acceleration cause the firing pin and/or release means(when present) to move axially towards the support element, to therebycrush the support element and position the firing pin in the armedposition, or freeing space for it to do so. The crushable supportelement may conveniently comprise a crushable washer. The forces ofacceleration experienced by a projectile on being fired from a weaponwill vary according to the particular projectile and weapon in question;however, these forces will typically range from 10,000 to 40,000 g andbeyond (wherein “g” represents acceleration due to gravity), and thecrushable support element, for example a crushable washer, should beengineered to withstand forces of acceleration accordingly.

[0021] The purpose of the frangible safety pin is also to prevent axialmovement of the firing pin from the safety position to the armedposition prior to firing of the projectile from the weapon, and operateson the same principles as the crushable support element. The safety pinthus engages the firing pin or release means (when present) prior tofiring, but is broken by axial movement of the firing pin or releasemeans (when present) under the forces of acceleration on firing theprojectile from a weapon. In a preferred embodiment, the safety pin isdisposed within the casing, and has a frangible inner portion whichextends inside the casing and engages and holds the release means suchthat the firing pin is held in the safety position. On firing theprojectile from a weapon, the forces of acceleration cause the releasemeans to move axially away from the initiator within the casing, to thusbreak the inner portion of the safety pin, and thereby no longer preventthe firing pin from moving axially within the casing from the safetyposition to the armed position.

[0022] The initiator of the projectile of the present invention may beany conventional initiator which when impinged by the firing pingenerates an explosive charge which can initiate detonation of thewarhead. Such initiators are well known to those skilled in the art. Aparticularly preferred initiator for use in the projectile of thepresent invention is disclosed in WO 99/51934, wherein the initiator isbiassed towards an armed position, but prior to firing is held in asafety position by the firing pin. On firing, the firing pin movesaxially away from the initiator, the initiator is urged from the safetyto an armed position, and is available to be impinged by the firing pinon impact with a target.

[0023] The projectile of the present invention preferably furthercomprises a back plate fitted to the rear of the casing, i.e.longitudinally opposite the warhead. The backplate is convenientlydiscoidal and may be fitted to the casing by a screw fitting. The backplate provides a shield against fin damage within the barrel of a weaponon firing of the projectile. Such damage may occur, for example, due todistortion of a cartridge sleeve surrounding the projectile within thebarrel, and may result in unreliable firing.

[0024] There is in principle no restriction as to the size of theprojectile of the present invention. For example, the projectile may bea small arms projectile, a mortar projectile, an artillery projectile,and the like. However, the projectile of the present invention isparticularly suitable for use with small arms.

[0025] Thus, in use the projectile of the present invention is placedwithin the barrel of a weapon for firing. Firing the projectile causesaxial movement of the actuating means within the casing, thus actuatingthe fin engaging means by exerting a radially outward force thereon.This radially outward force is transmitted via the fin engaging means tothe fins, thus causing the fins to move from a radially inward positionto a radially outward position.

[0026] The invention will now be described, by way of illustration only,with reference to the accompanying drawings in which:

[0027]FIG. 1 is a vertical cross-section view of the rear section of aprojectile prior to firing the projectile from a weapon.

[0028]FIG. 2 shows the same view as FIG. 1 showing the projectile afterleaving the barrel of a weapon.

[0029]FIG. 3 is an isometric view of the firing pin shown in FIGS. 1 and2.

[0030]FIG. 4 is an isometric view of the inner sleeve shown in FIGS. 1and 2.

[0031]FIG. 5 is an isometric view of the firing pin release means shownin FIGS. 1 and 2.

[0032]FIGS. 6a to 6 h are isometric views of the rear section of aprojectile according to the present invention showing a preferredassembly sequence of the fin engaging means.

[0033] N.B. In FIGS. 1 and 2 the initiator and warhead have been omittedfor clarity.

[0034] With reference to FIG. 1, the rear end of a projectile (10) isshown having a longitudinal casing (12). Externally mounted to therearward end of the casing are four fins (13), two of which are shown inFIGS. 1 and 2, via hinges (15). The four fins (13) are disposedequidistantly around the circumference of the casing (12). In FIG. 1 thefins (13) are shown in the radially inward position.

[0035] Disposed within the casing adjacent the inner wall thereof is aninner sleeve (14) which extends the length of the casing (12). The innersleeve (14) has an inwardly projecting flange (16) at the forward endthereof. Within the inner sleeve are disposed a firing pin (18), firingpin release means (20), and a crushable support member (22) in the formof a crushable washer. The firing pin (18) comprises a shaft (36)aligned along the axis of the casing, which shaft (36) has forward (38)and rearward (40) projecting portions. The forward portion (38) has aconical tip (42) which in use impinges on the initiator (not shown) onimpact of the projectile with a target. The firing pin (18) furthercomprises a frustoconical sleeve (44), which tapers outwardly towardsthe forward portion of the casing (12). The forwardmost portion of thefrustoconical sleeve has a surface (48) which is substantially parallelto the axis of the casing (12). The firing pin (18) is axiallyrearwardly biassed by a spring (46) which at one end engages the flange(16) and at the other engages and is fixed relative to the casing by theinner surface of sleeve (44).

[0036] A backplate (24) is attached to the rear end of the casing (12)by threaded flange (26), which backplate (26) supports the supportmember (22).

[0037] The release means (20) rests on the support member (22) and has acentral bore (21) therethrough within which the rearward portion (40) ofthe shaft (36) of the firing pin (18) rests, thereby supporting thefiring pin (18). The sides (23) of the release means (20) taper towardsthe forward end of the casing (12).

[0038] The inner sleeve (14) further includes longitudinal guide slots(28) within which are disposed fin engaging pins (30). One pin (30) ispresent per fin (13), i.e. four pins in total, although only two pins(30) are shown in FIGS. 1 and 2. The pins (30) have an outer conical end(32) and an inner hemispherical end (34). The outer end (32) of each pinengages a fin (13) adjacent the hinge (15) for greatest mechanicaladvantage, and the inner end (34) engages the outer surface of sleeve(44). Within, for example, a cartridge casing or the barrel of a weapon,the pins (30) are thus fixed in the radially inward position shown inFIG. 1 by the fins (13).

[0039] The casing (12) also comprises two safety pins (not shown)disposed therein, which project through corresponding holes (also notshown) in the casing (12) and inner sleeve (14). The safety pins (notshown) each have an inner portion which engages the release means (20).The safety pins (not shown) are disposed diametrically opposite eachother and equidistantly between two fins, perpendicularly to the axis ofthe casing (12).

[0040] Referring to FIG. 3, the firing pin (18) comprises a shaft (36)having forward (38) and rearward (40) projecting portions. The forwardportion (38) has a conical tip (42) which in use impinges on theinitiator (not shown) on impact of the projectile with a target. Thefiring pin (18) further comprises a frustoconical sleeve (44), whichtapers outwardly towards the forward portion of the casing (12). Theforwardmost portion of the frustoconical sleeve has a surface (48) whichin use is substantially parallel to the axis of the casing (12).

[0041] Referring to FIG. 4, the inner sleeve (14) includes longitudinalguide slots (28) within which in use are disposed fin engaging pins(30). The inwardly projecting flange (16) is not shown in FIG. 4. Theinner sleeve (14) further comprises further longitudinal slots (50)through which in use the safety pins (not shown) are disposed.

[0042] Referring to FIG. 5, the release means (20) has a central bore(21) therethrough within which in use the rearward portion (40) of theshaft (36) of the firing pin (18) rests, thereby supporting the firingpin (18). The sides (23) of the release means (20) taper towards theforward end of the casing (12), to allow the pins (30) to engage thesurface (44). The release means (20) further includes indents (52), bywhich in use the inner portions of the safety pins (not shown) engagethe release means (20).

[0043] Thus, FIG. 1 shows the rear end of a projectile (10) prior tofiring from a weapon. On firing from a weapon, the acceleration of theprojectile within the barrel of the weapon forces the release means (20)axially towards the rear of the casing (12). The release means (20)thereby breaks the inner portion of the safety pins (not shown) andcrushes the support member (22). The firing pin (18) remains in theposition shown in FIG. 1 when the projectile is within the barrel since,although urged towards the release means (20) by spring (46), the fins(13) are restrained in the radially inward position shown in FIG. 1 bythe inner wall of the barrel, which maintain the pins (30) in theradially inward position shown in FIG. 1, the inner ends (34) of whichengage the outer surface of sleeve (44), thus maintaining the firing pin(18) in the FIG. 1 position. However, on leaving the barrel, therestraint of the inner wall of the barrel is removed, and the spring(46) urges the firing pin (18) axially from the safety position of FIG.1 to the armed position shown in FIG. 2. Such axial movement of thefiring pin (18) causes the pins (30) to move radially outward withinguide slots (28) via the outer surface of the sleeve (44) and inner ends(34), and the outer ends (36) thus force the fins (13) radially outward.The firing pin (18) is held in the armed position shown in FIG. 2 by thespring (46). The fins (13) cannot return to the radially inward positionbecause the pins (30) are fixed in the radially outward position shownin FIG. 2 between the fins (13) and the forwardmost surface (46) of thesleeve (44). On reaching a target, the deceleration of the projectileprovides sufficient axial force in the forward direction that the firingpin (18) can overcome the bias of the spring (46) and can impinge theinitiator (not shown) to thereby detonate the warhead.

[0044] With reference to FIGS. 6a to 6 h, the fin engaging pins (30) maybe inserted as follows. FIG. 6a shows the rear section of a projectileprior to insertion of pins (30). The fins (13) are pivotally mounted tothe casing (12) by hinges (15). Each fin (13) has a hinge portion (54)adjacent the casing (12) through which a hinge pin (56) passes. Thehinge pins (56) are mounted to the casing (12) parallel to its axis. Thehinge portions (54) are substantially narrower than the length of thehinge pins (56) to allow the fins (13) to be axially slidable along thehinge pins (56). In FIG. 6a the hinge portions (54) are in an axiallyrearward position on the hinge pins (56). The hinge portions (54) extendfrom the fins (13) beyond the hinge pins (56) towards the casing (12),so that radial rotation of the fins (13) about the hinges (15) isrestricted when the fins are in the axially rearward position, i.e. asduring flight of the projectile, due to stopping of the hinge portions(54) by the casing (12). The casing (12) comprises indents (58) aroundits outer circumference aligned perpendicular to and beneath the hingepins (56) in an axially forward position. Each indent (58) extendslongitudinally along the casing (12) to an extent marginally greaterthan the width of each hinge portion (54).

[0045] For insertion of the fin engaging pins (30), the fins (13) aremoved axially forward along the hinge pins (56) to the position shown inFIG. 6b, i.e. such that each hinge portion (54) is in axialcorrespondence with an indent (58). In the axially forward positionshown in FIG. 6b, the fins (13) may be rotated in direction A, theindents (58) allowing rotation of the fins (13) about the hinge pins(58) beyond the radially outward position shown in FIG. 6a to theposition shown in FIG. 6c. The fins (13) are then moved axiallyrearwardly along the hinge pins (56) to the position shown in FIG. 6d toallow access to the guide slots (28). The fin engaging pins (30) arethen inserted into the guide slots (28), as shown in FIG. 6d. Once thefin engaging pins (30) have been inserted in the guide slots (28), thefins (13) are returned to the axially forward position, as shown in FIG.6e, and are rotated about the hinge pins (56) to the radially inwardposition shown in FIG. 6f. The fins (13) are then returned to theaxially rearward position, whilst being maintained in the radiallyinward position, as shown in FIG. 6g. The fin engaging pins (30) arethus inserted, and are ready for actuation of the fins (13) from theradially inward position to the radially outward position, as describedhereinabove. FIG. 6h shows the fin engaging pins (30) and fins (13) inthe radially outward position following actuation.

[0046] It will be understood that the illustrated embodiment describedherein shows an application of the invention in one form only for thepurposes of illustration. In practice the invention may be applied tomany different configurations the detailed embodiments beingstraightforward to those skilled in the art to implement.

1. A projectile for a weapon, which projectile comprises: an axiallymovable firing pin; an initiator actuable when impinged by the firingpin; a plurality of external peripheral fins movable from a radiallyinward position to a radially outward position when the projectileleaves the weapon; fin engaging means for moving each fin from theradially inward position to the radially outward position and formaintaining each fin in the radially outward position; and internalactuating means for actuating the fin engaging means to engage andthereby move the fins to deploy from the radially inward to the radiallyoutward position as the projectile leaves the weapon.
 2. A projectileaccording to claim 1, wherein the actuating means actuates the finengaging means by axial movement of the actuating means towards the finengaging means in response to the projectile leaving the weapon.
 3. Aprojectile according to claim 2, wherein the actuating means is biassedtowards the fin engaging means.
 4. A projectile according to claim 1,wherein the actuating means comprises the firing pin.
 5. A projectileaccording to claim 1, wherein the fin engaging means releasablyrestrains the firing pin in a safety position until actuation of the finengaging means, and which when actuated allows the firing pin to moveinto an armed position.
 6. A projectile according to claim 1, whereinthe fin engaging means comprises a pin per fin, each pin being disposedbetween a fin and the actuating means.
 7. A projectile according toclaim 6, wherein each pin has a hemispherical inner end for engagementwith the actuating means, and a conical outer end for engagement with afin.
 8. A projectile according to claim 1, which further comprises meansfor disengaging the fins from their radially outward position to allowaccess to the fin engaging means.
 9. A projectile according to claim 1,which further comprises a casing, which casing has an inner sleevetherewithin adjacent the inner wall thereof for guiding movement of theactuating means and fin engaging means.
 10. A projectile according toclaim 9, wherein the inner sleeve includes longitudinal slots withinwhich the fin engaging pins are disposed.
 11. A projectile according toclaim 9, wherein the inner sleeve provides means for fixing a means forbiassing the actuating means to the casing.
 12. A projectile accordingto claim 1, which further comprises a firing pin release means and acrushable support element on which the release means is supported, whichrelease means is axially moveable towards the support element.
 13. Aprojectile according to claim 1, which further comprises a back platefitted to the casing longitudinally opposite the warhead.
 14. Aprojectile according to any preceding claim 1, which further comprisesmeans for moving the fins from the radially outward position to aposition which provides improved access to the fin engaging means overthe access provided to the fin engaging means when the fins are in theradially outward position.
 15. A projectile according to claim 14,wherein the means for moving the fins comprises a hinge along which thefins are axially movable from a first position to a second position,whereby radial movement of the fins in the second position is lessrestricted than radial movement of the fins in the first position.
 16. Aprojectile according to claim 1 which is a small arms projectile for asmall arms weapon.
 17. Cancelled.
 18. A method for assembling aprojectile according to claim 15, which method comprises the stepsmoving the fins in the radially outward position form the first positionto the second position, moving the fins radially to the position whichprovides improved access to the fin engaging means, applying the finengaging means to the projective, moving the fins to the radially inwardposition, and returning the fins in the radially inward position to thefirst position.
 19. Cancelled.